1. Field of the Invention
This invention relates to a semiconductor encapsulating epoxy resin composition which cures into products having improved adhesion and moisture resistance and semiconductor devices encapsulated with such cured products.
2. Prior Art
Most advanced semiconductor devices are of the resin encapsulation type which is advantageous in large scale manufacture and thus offers low cost products as compared with the prior art ceramic and can sealed types. Prominent among the encapsulating resins are epoxy resins having excellent electrical and physical properties.
Semiconductor devices encapsulated with resins, typically epoxy resins, however, are less resistant against humidity as compared with the ceramic and can sealed ones and often suffer from entry of water through the resin-frame interface.
Also, ionic impurities including hydrolyzable chlorine are left in encapsulating resins. These impurities interact with water to increase the current leakage of semiconductor devices and cause corrosion of aluminum electrodes, both leading to a lowering of reliability.
Many attempts were made for eliminating the defects associated with the relatively low moisture resistance of epoxy resin-encapsulated semiconductor devices. For example, it was proposed to remove ionic impurities from encapsulating materials and to add thereto an additive capable of trapping ionic impurities. However, it was substantially impossible in practice to ensure complete removal or trapping of ionic impurities. These approaches failed to attain the intended purposes.
Another known approach for improving the moisture resistance of encapsulating resins is to blend silane coupling agents. The known silane coupling agents for use in epoxy resin compositions for encapsulating semiconductor devices are epoxy silanes, mercapto silanes, amine silanes and unsaturated hydrocarbon silanes. Typical of the mercapto silanes is 3-mercaptopropyltrimethoxysilane which gives off an offensive odor and is undesired for practical use. One exemplary amine silane is N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane which detracts from the shelf stability of resin compositions containing it. The unsaturated hydrocarbon silanes include, for example, vinyltriethoxysilane and 3-methacryloxypropyltrimethoxysilane which are free of a functional group reactive with phenol-curable epoxy resins and thus cannot fully exert their function as a coupling agent. Useful examples of the epoxy silane are 3-glycidoxypropyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane which are free of the above-mentioned problems, but insufficient in adhesion and moisture resistance improvement.
Therefore, an object of the present invention is to provide a semiconductor encapsulating epoxy resin composition having improved adhesion and moisture resistance, especially moisture resistance after a moisture absorption and soldering test. Another object of the present invention is to provide a semiconductor device encapsulated with such an epoxy resin composition in cured state.